Phenylketonuria (PKU): Symptoms, Causes, Treatment

A newborn may appear healthy despite elevated phenylalanine. A positive screening result needs prompt confirmatory assessment and metabolic-team planning; it does not necessarily mean symptoms or established injury are present.

Related reading: Avoiding malnutrition during therapeutic diets.

Without treatment, development, learning and behavior may be affected, and seizures or skin problems can occur. Do not wait for symptoms after an abnormal screening result.

The usual cause is inherited changes affecting the enzyme that processes phenylalanine, following a recessive pattern. The disorder is not caused by the family’s choice of milk or a feeding mistake.

Risk is increased when both parents carry the causative variant, although they may have no symptoms. Counseling and selected sibling testing help; absence of a family history does not exclude PKU.

Confirmation uses amino-acid measurements and appropriate tests to distinguish causes of high phenylalanine, sometimes including genetic analysis. Repeated blood levels guide treatment rather than appearance or symptoms alone.

Phenylalanine allowance, medical foods and protein substitutes are individualized. Specialist medicines may help depending on response and eligibility. Do not independently stop protein or breastfeeding; growth requires balanced intake and a monitored feeding plan.

Uncontrolled levels can harm development and cognitive function and may affect a fetus carried by an affected mother. An unbalanced restrictive diet can also cause deficiencies, so a list of forbidden foods is insufficient.

Follow team advice on food labels and aspartame, blood monitoring and prescribed medical foods. Control before and during pregnancy is important to protect the fetus even if the baby does not inherit PKU.